Coupler plugs of the aforementioned type are usually designed for the connection between a cable harness plug and a lambda probe, the connections in the coupler plug being provided for adjustment, signal, and/or heating of the probe. The lambda probe and the lambda control, in connection with three-way catalytic converters, represent today an effective method for cleaning exhaust emissions. The lambda probe, which, for example, can be inserted into an exhaust system, includes a sensor for determining the oxygen content in the exhaust gas.
The residual oxygen content is well suited for use as a measured quantity, and it regulates the air-fuel ratio, because it indicates precisely whether the air-fuel mixture is being completely combusted.
In this context, the lambda probe supplies a voltage signal, which represents the momentary value of the mixture composition and which follows the mixture changes. The fuel supply to the engine is controlled by a carburation system in accordance with the signal from the lambda probe in such a way that a stochiometric air-fuel ratio λ=1 is achieved. Heated or unheated probes are used in accordance with the design of the exhaust gas system and the conditions in which they are used. Outside the field of motor vehicles other applications of the lambda probe include, e.g., regulating gas motors or oil/gas burners.
In particular, broadband lambda probes are designed in modular form and, in combination with planar technology, facilitate the integration of a plurality of functions. They usually have functional layers, which are made up of a porous protective layer, an external electrode, a sensor film, an internal electrode, a reference gas channel film, an insulation layer, a heating element, a heating film, a resistor or adjustment element, and connection contacts.
Because broadband lambda probes are made up of the combination of a nernet concentration cell (=sensor cell) and a pump cell that transports oxygen ions, it can measure very precisely, not only in the stochiometric point at λ=1, but also in the lean and rich mixture ranges.
Every probe must be individually adjusted. For this purpose, the probe has a built-in resistor (“mini-hybrid”). The adjustment, which is advantageously performed using a laser beam, is made by properly ablating the resistance layer made up of a ceramic substrate, thereby inducing a change in the resistance, so that an adjustment follows.
One specific embodiment provides for the adjustment unit, i.e., the resistor, to be mounted directly at the probe. A further exemplary embodiment provides for the resistor to be accommodated externally, for example, on a cable harness plug that is coupled to the probe.
To prevent the ingress of humidity, contamination or the like into the coupler plug, and to assure that the appropriate atmosphere prevails within the coupler plug, the cover element has additional seals. Furthermore, pressure equalizer elements are mounted on the housing of the coupler plug. In addition, so-called primary locking mechanisms are also provided on the cover element. They ensure that even when the cable harness plug is subjected to strong vibrations, the cover element is firmly seated in the base element.
In addition, secondary locking elements are provided, which offer additional reliability especially in response to powerful stresses.
One disadvantage of the design of the coupler plug discussed here can be seen, in particular, in that it is necessary to mount secondary locking elements in different working and assembly steps.
In addition, it is necessary to manufacture, in particular, the secondary locking elements in a separate manufacturing process.